1. Field of the Invention
The present invention relates to a flow rate measuring apparatus suitable for measuring a flow rate of a fluid such as sewage, human waste, sludge, or organic drainage which tends to produce an adhesive substance on a pipe and, more particularly to a flow rate measuring apparatus capable of removing an adhesive substance on a measuring pipe without removing pipes.
2. Description of the Related Art
Various types of flow rate measuring apparatuses are used in various places. An example of the places in which the flow rate measuring apparatus is used is a sewage disposal plant. In the sewage disposal plant or the like, various types of substances adhere on the inner surface of the measuring pipe (if the measuring pipe has a lining, the inner surface of the lining) of a flowmeter due to properties of a fluid whose flow rate is to be measured. When the flowmeter is an electromagnetic flowmeter and an adhesive substance has high conductance, the adhesive substance resistively connects electrodes for detecting an induced electromotive force and decreases an indication value of the flowmeter. This adhesive substance deteriorates over time due to bacteria, microorganisms, or the like into a hard cement-like substance consisting of carbon, minerals, and the like in the adhesive substance. Layers of this cement-like substance strongly adhere on the inner surface of the measuring pipe and therefor cannot be easily removed.
In addition, when an adhesive substance decays in summer time, the adhesive substance sometimes deteriorates into a bread-like substance due to a gas generated upon decay. This bread-like adhesive substance hardly transmits an ultrasonic wave. For this reason, when the flow rate measuring apparatus is an ultrasonic flowmeter, it is difficult to perform measurement, or a measurement error occurs. Such a bread-like substance also deteriorates into a hard substance over time and therefore cannot be easily removed.
Such an adhesive substance also poses various problems in a flowmeter except for the electromagnetic flowmeter or the ultrasonic flowmeter. For example, an effective area of a measuring pipe is reduced, and a measurement value error occurs.
These problems are not limited to sewage but arise for an type of fluid although a degree of the problem differs.
For this reason, this adhesive substance must be removed while it can be easily removed. Since, however, a measuring pipe is connected to a pipe system, it is difficult to clean the inner surface of the measuring pipe. Examples of a conventional technique of removing an adhesive substance in a measuring pipe without removing the measuring pipe from a pipe system are: (1) a method of blowing a cleaning solution against electrodes of an electromagnetic flowmeter and their peripheral portions to remove an adhesive substance (Japanese Utility Model Publication No. 57-59937); and (2) a method in which a porous substance is used as a lining material of a measuring pipe and a cleaning solution is injected to remove an adhesive substance (Japanese Utility Model Publication No. 57-49779). In these techniques, however, since electrodes and their peripheral portions of an electromagnetic flowmeter are mainly cleaned, only a part of an adhesive substance can be removed. Therefore, (1) a problem in which electrodes of an electromagnetic flowmeter are resistively connected, (2) a problem in which transmission of an ultrasonic wave is interfered, and (3) a problem in which an effective area of a measuring pipe is reduced are basically left unsolved. In addition, in the above cleaning methods, a measuring pipe must be emptied upon cleaning in order to achieve a sufficient cleaning effect, resulting in an inconvenient operation.